Rapid transit systems such as the New York City subways, London Underground subways, the San Francisco Municipal Railway and BART systems are all powered by electricity supplied either through third rail shoes or pantagraphs reaching overhead wires, supplying power for driving motors, heating, lighting and air conditioning.
This invention concerns a parallel electrical wiring system, called train lines, carrying alarm signals throughout the train, to announce loss of braking air pressure, a wheel bearing hot box, or other malfunctions, to indicate status such as "all doors closed", or to power public address speakers, or to control air conditioning or heat, "turn interior lights on", etc. These train lines extend the length of each car, and are connected to each adjacent car through an electrical "coupler", i.e., a connector having a plurality of electrical connection points in "left" or "right" types for mating with a coupler in a coupled car. The electrical connection points are usually called "pins" regardless of type of connection.
Various manufacturers design cars having a fixed coupler at both ends which permit coupling at either end, without regard to the orientation of the car with respect to other cars in the train. A train is typically made up of several cars connected together. Each car typically has a motor and a driver's panel at each end. The train can be driven from any car, provided it is placed at the front of the train. Each electrical coupler is of the type which has two halves, each half being a mirror image of the other half. This type of electrical coupler permits similar cars to be coupled together in any 180.degree. orientation.
Some electrical couplers with mirror image pairs of coupler pins have only one physical housing for both left and right pairs of pins. The most common arrangement, however, is for each mirror image half to be in a separate physical housing called a coupler head or electrical coupler head and is usually identified as right or left (as if someone inside the train were looking out). The electrical connection points comprise two types of physically mating metal devices. Both mating halves are usually called "pins" regardless of type. The coupler "pins" perform a function which is analogous to the function performed by the sockets and pins in a manually installed connector; however, the coupler "pins" are physically different. "Pins" are usually of fixed and moveable types wherein moveable types are backed by springs and fixed pins are solidly mounted. Fixed pins mate to moveable pins. Sometimes, coupler heads do not have all the same type of pins. That is, the same coupler head (mirror image half) may have both fixed and moveable pins.
As mentioned, train lines are wires which run from one end of a train to the other, through the electrical couplers. Train lines must be connected to a right and a left coupler pin at both ends of the car. This is necessary, according to the present state of the art, to allow the function of the train line to be unchanged if the car is rotated 180.degree.. This requires four coupling connections per train line per car.
Coupler pins are expensive and must be kept to a relatively small number for mechanical reasons. There is also, on occasion, the need to add new train lines on existing cars which, it may unfortunately be found, do not have enough coupler pins available. It should be noted that the above-mentioned four pin coupling requirement does not exist for cars that are only allowed to couple in the same 180.degree. orientation, or for special train lines which change function when the car is rotated. It should also be noted that sometimes cars are grouped in groups of two or three or more with permanent connections between cars. In that case the coupler heads at the ends of the group are treated as if at the ends of a single car at least for purposes of temporary coupling (non-permanent attachment).